Recently, automobile ownership per household has increased due to such advantages as convenient long distance travel and quick transportation. As a result, there are more than 17 million automobiles in the country and 7.25 billion (725,000,000) worldwide, which means that the automobile ownership per household is equal to or greater than one.
The increase in the number of automobiles has caused a corresponding increase in the consumption of fuel such as gasoline, diesel oil, liquefied petroleum gas (LPG). However, the reserves of oil resources are finite. Accordingly, there is a growing concern that, should the current trend oil consumption continue, oil resources will be exhausted in over half a century. Moreover, exhaust fumes from automobiles are a primary cause of air pollution and thus are responsible for various environmental issues such as global warming.